WO 99/04870 describes an expansion of the skis' width and length with the help of a “tip shape modifier” and a “tail shape modifier”. These parts are being mounted to the skis in front of and behind the binding respectively, and thus make the skis better suited for downhill skiing in deep powder snow. The two parts are each divided into several sections, which are being attached to each other and to the skis. These can be taken on and off the skis according to changing conditions, and be carried in a backpack. This may not be a bad idea, but it seems after all to be somewhat complex and cumbersome in use. And the ski edges have to be completely straight, without any side cut where the sections are to be threaded onto the skis lengthwise.
NO 309928 has the gripping surface as a part of the actual ski. It goes along the most of the outer side of the ski base/sliding surface, and constitutes about ¼ of the ski width. The gripping surface is elevated and parallel to the sliding surface, and is equipped with skins or other gripping agents. So to get grip, also here stepping a bit over onto the outer side of the foot is required. An advantage with this solution compared to my own, is that nothing is added to the skis' weight or width, and they retain their suitability for ski tracks. And the bottom outer edges of the skis will still be useable for breaking or swinging. But for good reasons, the gripping surface is here parallel to, and not oblique to the sliding surface. A result of this should be that the grip in hard and icy conditions will hardly be so good, because only the outermost part of the gripping surface should then be in contact with the substrate. To avoid losing too much of the ski's support surface, the gripping surface can not constitute more than about ¼ of the ski width, which makes the possibility of a quite large gripping surface with much grip rather limited. And the skis have to be reworked, which can be quite inconvenient as well as its adding much cost to the skis. For no major ski producers have been willing to produce these skis, and the ski reworking is a one-man enterprise on the inventor's home place.